The central objective of this Program Project is to use the structure of the gp120/CD4/mAb17b complex and structure-based mimetics to design antagonists of the interaction of HIV-1 with human cells. T-cell docking and entry by HIV-1, a major route of cell infection in AIDS, is driven by specific recognition of T-cell surface protein CD4 and chemokine coreceptor by HIV envelope protein gp120. The crystallographic structure of CD4 is known, as is its complex with gp120 and the coreceptor surrogate antibody 17b. The structural nature and interrelationship of gp120 binding sites for CD4 and coreceptor have been revealed. The advancing high-resolution structural understanding of the protein participants in virus-cell recognition together with the advancing technology of mimetics design make it possible to combine structure determination, modeling, miniprotein engineering, organic synthesis and thermodynamics analysis to design new antagonists for HIV- 1 infection as well as to elucidate recognition mechanisms in the gp 120/CD4/coreceptor molecular network. The specific aims of this proposal are: (1) identify binding sites in the CD4-gp120 and gp120-coreceptor interfaces by computational modeling of existing high-resolution structures and structural predictions of the protein partners; (2) transplant CD4, gp120 and coreceptor/l7b binding site structural elements into conformationally constrained miniprotein constructs by chemical and recombinant DNA approaches to obtain miniprotein mimetics and use these to define the minimal structural elements driving formation of the interaction network; ( 3 ) generate peptidyl and nonpeptidyl probes of CD4-gp 120 interface via structure-driven and diversity- driven design schemes; (4) characterize the thermodynamics of recognition in the gp 120/CD4/coreceptor network and develop thermodynamic guidelines for design of gp 120 antagonists that maintain activity against naturally occurring polymorphisms and potential drug-resistant HIV-1 mutants; ( 5 ) utilize key structural elements as determined from high resolution structure, modeling, thermodynamics, miniproteins and constrained peptidomimetics to design small molecule CD4 antagonists for HIV infection and AIDS pathogenesis. structural driving forces of HIV-1 envelope attachment with host cell receptors and new drug candidates for AIDS. Long term, the mimetics strategies derived will be useful to design antagonists of other interactions, such as gp120- gp41 and gp120-DC-SIGN, that also are associated with human cell-HIV-1 attachment and viral entry. Overall, this project will yield technologies for protein mimetics construction, advanced definition of key.